I have had the same thing happen so it must be a pretty common occurrence. Mine looked like the intake to an AC filter and it was enough to restrict some air flow through the radiator. This debris could not be removed by spraying water from the front or rear through the radiator. It could only be removed by removing the cooling fans and taking the AC condenser loose to allow access to the front of the radiator to remove the fine debris.
Your right. There is no way but again how does one know this is their problem. Couldn't see it till we removed the MH from around it. LOL No the pressure washer did not remove all of it by spraying thru the frt. and back. There appears to be no easy way to solve this.
CharWan